1. Field of the Invention
The present disclosure relates to a fuel cell system and a method for deactivating the fuel cell system.
2. Discussion of the Background
A fuel cell has an anode and a cathode and generates electric power by being supplied with hydrogen (i.e., fuel gas) to the anode and air containing oxygen (i.e., oxidant gas) to the cathode. When the electric-power generation in the fuel cell is to be stopped, if the oxygen remains in the cathode system, the cathode is known to become in a high potential state when hydrogen is supplied to the anode at the time of subsequent activation. The high potential state at the cathode is known to cause deterioration in a solid polymer electrolyte membrane that constitutes the fuel cell.
Therefore, when stopping the electric-power generation in the fuel cell, so-called oxygen-consumption electric-power generation is performed for consuming the oxygen remaining in the cathode system of the fuel cell so as to reduce the oxygen concentration in the cathode system and to set the interior of the cathode system in a nitrogen-rich state, thereby preventing the cathode from being in a high potential state at the time of subsequent activation.
For example, Japanese Unexamined Patent Application Publication No. 2003-115317 discusses a technology in which the electric-power generation in the fuel cell is stopped after setting the interior of the cathode system in a nitrogen-rich state by performing so-called exhaust-gas recirculation electric-power generation. In this exhaust-gas recirculation electric-power generation, electric power is generated by circulating air off-gas discharged from the cathode of the fuel cell to the cathode again. In this case, the oxygen-consumption electric-power generation is performed based on the exhaust-gas recirculation electric-power generation.